2019

1.

A.

In the (now obsolete) subnetting scheme with non-contiguous masks, consider the network 201.91.217.0/24, subnetted with a subnet mask of 255.255.255.170

I. (2p)

Give the subnet mask as a bitstring of length 32

11111111 11111111 11111111 10101010

(128 + 32 + 8 + 2 = 170)

II. (2p)

How many subnetworks and how many hosts in each subnetwork are available?

Fuck this question
Answer says 14 of each

III. (2p)

No

B.

I. (2p)

Bipartite graph, routers on the left lans on the right

II. (2p)

Now suppose we replace R0 with a switch S. What does the (Layer 3) bipartite graph now look like?

A switch is a layer 2 device, so it will simply not show up in the layer 3 view, especially since it's not connecting anything else

C. (2p)

What are the two purposes an IPv4 address can have?
Specify to which layer each of those purposes belongs.

An IPv4 address can be used as both a locator and identifier
Both are used in L3 (as IP is L3)

D.

Not relevant

2.

A.

Consider the following IPv6 networks:
2019:1217:1230:b123::/64
2019:1217:1230:b124::/62
2019:1217:1230:b144::/63

I. (2p)

What is the value of bits 0, 10, 20, 30 and 40 in these networks?

0: 1st bit of group 1 -> 1st digit bit 1
10: 10th bit of group 1 -> 3rd digit bit 2
20: 4th bit of group 2 -> 5th digit bit 4
30: 14th bit of group 2 -> 8th digit bit 2
40: 8th bit of group 3 -> 10th digit bit 4

0: 2 = 0010 -> 1st bit = 0
10: 1 = 0001 -> 2nd bit = 0
20: 1 = 0001 -> 4th bit = 1
30: 7 = 0111 -> 2nd bit = 1
40: 2 = 0010 -> 4th bit = 0

Since this only concerns bits from the first three segments, which are identical between the networks, the above applies to all three networks

II. (6p)

What are the next bits, after the first 56 bits that belong to these prefixes?
Specify this for each of the three networks separately

56 bits -> 56 / 4 = 14 -> so from character 15

III. (2p)

What is the IPv6 network (in prefix notation) with the largest possible prefix that includes all of these three networks?

2019:1217:1230:b1::/57

B.

I. (1p)

What is the IPv6 prefix used for unique local unicast?

fc00::/8

II. (2p)

What is the IPv6 prefix used for multicast?

ff00::/8

III. (1p)

How is IPv6 multicast restricted to the link layer?

Not covered

C.

Not relevant

D.

IPv6 does not use ARP

I. (2p)

What is the protocol called that IPv6 uses for ARP functionality?

It is called the Neighbour Discovery Protocol (NDP) and uses on ICMPv6

II. (2p)

What ICMPv6 types are used for this functionality, give name or number

The used types are:

3.

A.

Not covered

B.

Not covered

C.

STP, again

D.

  1. Bottom left has no root port, so it is the root bridge with ID 1

  2. Top center network chose center over top left
    Center right network chose chose center over bottom right
    Right network chose top right over bottom right

    C < TR < BR
    C < TL

    So out of these 4, center must be the lowest which is 2

  3. We know that BR is not 5, so it must be 3 or 4
    TR must be lower than BR
    Thus TR is 3 and BR is 4

  4. Only 5 is left for TL

4.

A.

Consider the abstract routing tree, with root X at depth 0 and nodes labelled with binary sequences of 0s and 1s

I. (2p)

Suppose you want to run RIP in this tree, what is the maximal depth of the tree to make this possible

RIP can run with max 15 hops, so the max depth would also be 15

II. (2p)

We can consider each binary number to an extra step of going either left or right

The common prefix is 10

So from 10011 up to 10 is 3 steps, and then down to 101111 is down another 4 steps
So a total distance of 7

B.

What are the default values for update timer, invalid timer and flush timer?

Update: 30s
Invalid: 180s
Flush: 240s

C.

What part of the RIP routing table is NOT communicated through RIP updates?

Gateways / next-hop

(This is done in RIPv2 though)

D.

What feature of RIPv2 is NOT supported by RIPng?

Authentication (by using a fake route entry)